Hook with screw for treatment of vertebral column deformities

ABSTRACT

This hook serves to treat vertebral column deformities. It is comprised of a shaft portion (2) with a longitudinal axis (1) to which a longitudinal support rod (5) can be attached transversely to the longitudinal axis (1), as well as a hook body (3) with a convex posterior side (34) and a concave anterior side (35) bent away from the longitudinal axis (1) connecting to the shaft portion (2). It is provided with a penetrating drill hole (36) extending from the convex posterior side (34) to the concave anterior side (35), to accept a screw (4).

This invention relates to a hook for correction of spinal deformities.

It is often necessary to treat thoracic vertebral column deformitiessurgically. The anatomy of the vertebral column must be restored andmaintained. For this, fixation systems are used either dorsally orventrally. Dorsal systems generally consist of at least one longitudinalsupport, but most have a left and a right support, and individualanchoring elements. The latter form a load-transferring connectionbetween the vertebral column and the longitudinal support.

Currently there are three possibilities known for connecting thelongitudinal support to the vertebral column: wire cerclages, pedicularscrews and vertebral column hooks.

The wire cerclages are placed along the lamina and the spinous processesof the spinal vertebrae. There is a certain risk connected with theattachment of wire cerclages for the patient, since they may injure thespinal cord. In addition, the wires may, over time, cut through thebones (high local tension peaks cause resorption of the bones under thewire) or may simply break.

Pedicular screws are generally screwed through the pediculus into thevertebra. The pediculi are very narrow in the upper thoracic vertebralcolumn and difficult to locate due to the deformity. The use ofpedicular screws in this area therefore poses a high risk. In addition,many surgeons generally avoid using pedicular screws in the area of thethoracic vertebral column.

Vertebral column hooks are currently the elements most often used.Depending on the situation, they are placed on the lamina, the pediculusor the transverse process of the vertebrae. In contrast to the wirecerclages, they offer the advantage that the stress is transferred to arelatively large area of the bone and accordingly there is hardly anybone resorption at the point of contact between bone and hook. The hookshave, however, in contrast to the pedicular screws, the majordisadvantage that they can transfer stress to the longitudinal supportonly when they are pressed firmly against the bone. With current systemssuch an initial load can be applied only through the longitudinalsupport. This makes it very difficult to manipulate the vertebrae in thearea of the deformity with currently known hooks. The invention isintended to create remedial measures here. The invention is based on thetask of creating a hook firmly and stably connected to the vertebra.

These difficulties are overcome or ameliorated by means of a hookcomprising a shaft portion having a longitudinal axis, receiving meansfor seating a support rod positioned transversely to the axis and acurved hook body having a first end connected to said shaft portion, asecond free end, and a curved section connecting said first and secondends forming a bight between the first end and the second end, and ahole in the curved section of the curved hook body adjacent the firstend, the hole having a central longitudinal axis extending into thebight at an angle to the longitudinal axis.

Pedicular hooks pursuant to the invention are suitable, in particular,for thoracic application. Due to the additional screws insertablethrough the hook shaft, the pedicular hook can be pressed firmly intothe osseous seat. The screw here is introduced from the caudal to thecranial (at an angle of approximately 120°-125° to the longitudinal axisof the pedicular hook) through the hook shaft into the main mass of thefacet joint or to the corresponding vertebra. Thus, the pedicular hookcan transfer forces and torque like a pedicular screw without slippingout from its osseous anchorage, which forms the precondition for theexecution of a segmental correction.

There are many other advantages to the invention:

Due to the independent, stable connection of the hook according to theinvention with the vertebra, the hook can be manipulated individually;

The vertebral column deformity to be treated can be corrected step bystep from the less deformed side;

The assembly of the hook is more sure in the thoracic range than theinsertion of pedicular screws, since the hooks serve simultaneously asthe drilling guides for the bone screws;

The hook can be pressed optimally into the osseous site based on thesloped position of the bone screws.

The fastening of the hook pursuant to the invention to the longitudinalsupport, within a vertebral column fixation device, may be handled inmany known ways. For this purpose, the shaft portion of the hookpursuant to the invention has corresponding design elements that permitconnection to the longitudinal support, for example as disclosed in EP-A0 348 272.

The clinical application of the hooks pursuant to the invention isanalogous to those known systems and is described in detail in J.Debousset and Y. Cotrel, Orthopade (1989) 18:118-127 "TheCD-Instrumentation in der Behandlung von Wirbelsaulendeformitaten [CDInstruments in the Treatment of Vertebral Column Deformities].

Methods of embodiment of the invention that simultaneously explain thefunctional principle are shown in the drawings and described in greaterdetail below, where, in all drawings, a pedicular hook is shown as themethod of embodiment.

FIG. 1 shows a longitudinal view through the pedicular hook pursuant tothe invention;

FIG. 2 shows a partial view through the pedicular hook pursuant to theinvention with a screw inserted;

FIG. 2A shows a partial view through the pedicular hook pursuant to theinvention with a modified screw;

FIG. 3 shows a partial view through the pedicular hook pursuant to theinvention with a modified screw; and

FIG. 4 shows a lateral view of the pedicular hook pursuant to theinvention implanted in the vertebrae.

The pedicular hook shown in FIG. 1 in detail consists essentially ofshaft portion 2 that can be fastened to longitudinal support rod 5 and acurved hook body 3 connected thereto. The curved hook body has a firstend connected to the shaft portion, a second free end and a curvedsection forming a bight 35.

Shaft portion 2 consists of a connecting device that is described ingreater detail in the patent application published under No. EP-A1 517059.

It consists essentially of external element 22 with a circularcylindrical drill hole 21 and internal element 23 rotatable around axis1 and displaceable in drill hole 21. Both elements 22 and 23 have twopenetrating openings 24 and 25 jointly forming a channel transverse toaxial direction 1 of the two elements 22 and 23 to accept longitudinalsupport rod 5. If longitudinal support 5 is introduced into the twodrill holes 24 and 25, the axial displaceability of internal element 23in drill hole 21 of external element 22 is blocked in one direction andits rotation is restricted to the angle range of through openings 24 and25 of the two elements 22 and 23. Internal element 23 can be elasticallydeformed due to its through opening 25 in comparison to its axis 1, and,moreover, has external threading 26 which cooperates with nut 27. Incase of axial tension on internal element 23 via nut 27, which causes anaxial displacement of internal element 23 relative to external element22, expansion of the elastically deformable internal element 23 occursand tension on the same inside drill hole 21 of external element 22 withsimultaneous blockage of the entire connection device and longitudinalsupport rod 5 inserted therein. Nut 27 is tightened or loosened via twoinstruments (not shown in the drawings), a socket wrench and a suitableinstrument that holds the pedicular hook in place when manipulating nut27. This instrument is introduced into longitudinal slot 28 of nut 27like a screwdriver.

Through opening 25 is constructed with the advantage that longitudinalsupport 5 need not necessarily run parallel to hook body 3. Thisprevents the hook pursuant to the invention from being unnecessarilystressed with screw 4 during the assembly of longitudinal support rod 5,which conceals the danger that screw 4 may be torn from its anchoring inthe bone. In the case of severe scolioses, a 100% correction isfrequently impossible. In these cases, it is advantageous to have hookswith a through opening perpendicular (instead of parallel) tolongitudinal support rod 5. To create this, drill hole 21 of shaftportion 2 is arranged at a right angle to hook body 3 instead ofparallel to it, to accept a longitudinal support spacer (or transversesupport) with an enlarged profile, that has a through opening to acceptthe actual longitudinal support. Via this longitudinal support rodspacer it is possible to connect longitudinal support 5 with the hooknot only centrally but rather at a certain distance from longitudinalaxis 1. The through opening in the longitudinal support spacer can beclosed or open and can be constructed in such a manner that thelongitudinal support spacer can be rotated a certain amount withreference to hook body 3. The advantage of this method of embodiment(not shown in the drawings) is grounded in the fact that by this means,unnecessary forces during assembly of the longitudinal support spacercan be avoided.

Instead of the above-described, preferred connecting device for shaftportion 2, any other known connecting system can be used to fix shaftportion 2 to longitudinal support 1, for instance, pursuant to EP-A1 348272.

Hook body 3 is convex on its posterior side 34 and bifurcated at itsfree end 31. The two legs 33 form bay 32 adapted to pedicular geometry.The length of the two legs 33 can be different, as described in detailin the European Patent Application published under No. EP-A1 0 517 059.Bent-away free end 31 of hook shaft 2 runs essentially perpendicular tolongitudinal axis 1.

At convex posterior side 34 of hook body 3, through drill hole 36extending to curved section forming a bight 35 is provided to accept ascrew 4. The longitudinal axis 39 of drill hole 36 preferably lies at anangel α of 115 to 130 degrees, preferably form 120 to 125 degrees to thelongitudinal axis 1, and extends to said bight 35.

As shown in FIG. 2, drill hole 36 can have cylindrical section 37 toaccept screw 4 provided with cylindrical head 41. Instead, as shown inFIG. 3, drill hole 35 can also have spherical section 38 to accept screw4 with spherical head 42. The method of embodiment with sphericalsection 38 permits, within certain limits, a spatial displaceability ofscrew 4, indicated by arrow 43; meanwhile, in the method of embodimentwith cylindrical section 37, screw 4 is introduced.

Drill hole 36 can also be formed conically with a similar effect as withcylindrical screw 4, as shown in FIG. 2A.

Drill hole 36 can, as shown in FIG. 2, have a thread 40, whichcorresponds, at least in slope, to thread 44, of screw 4. In this case,it is possible to hold concave anterior side 35 of hook body 3 at aprecisely defined distance from the bone. A further advantage of thismethod of embodiment consists in the fact that screw 4 is tensioned inthe hook by tightening. This prevents screw 4 from unscrewing itselfover time from the bone. In the other methods of embodiment, theunscrewing of screw 4 is impeded by the fact that the screw head (41,42) is placed directly under longitudinal support rod 5.

As shown in FIG. 4, the pedicular hook pursuant to the invention isinserted between lower facet joint 64 of vertebra 6 and upper facetjoint 81 of vertebra 8 distanced by ligament disc 61 and lying under it,whereby hook body 3 from the caudal side embraces pediculus 63 due toits forked formation. Bone screw 4 is anchored in lower facet joint 64of vertebra 6 and penetrates or contacts up to four cortical zones,depending on their length (71, 72, 73, 74).

Segmental correction in scoliosis is considered the main indication forthe use of this method of embodiment. The goal of scoliosis treatment isto bring the vertebra toward the longitudinal support and tocounter-rotate the twisted vertebra. In the devices pursuant to thestate of the art, this occurs in such manner that the vertebral columnis corrected in one single step, by rotating the longitudinal supportfrom the anterior plane to the sagittal plane (so-called globalcorrection). With this method of correction the counter-rotating torqueapplied to the vertebral column is very slight, since the caudal hooklying on the apex vertebra must be hooked into the lamina and thus liespractically over the rotational center.

It is claimed:
 1. A hook for the treatment of vertebral columndeformities comprising:a shaft portion having a longitudinal axis, achannel in said shaft portion transverse to said longitudinal axis forseating a support rod; a curved hook body having a first end connectedto said shaft portion, a second free end, a curved section connectingsaid first and second ends forming a bight between said first end andsaid second end, and a hole in said curved section of said curved hookbody adjacent said first end, said hole having a central longitudinalaxis extending into said bight at an angle to said longitudinal axis. 2.The hook of claim 1, characterized in that the central axis of the holeincludes an angle of 115 to 130 degrees to the longitudinal axis of theshaft portion.
 3. The hook of claim 2, wherein the angle is from 120 to125 degrees.
 4. The hook of claim 1, characterized in that the hole hasa cylindrical section adapted to accept a screw provided with acylindrical head.
 5. The hook of claim 1, characterized in that the holehas a spherical section adapted to accept a screw provided with aspherical head.
 6. The hook of claim 1, characterized in that the holehas at least in part a threading adapted to received a threaded screw.7. The hook of claim 1, characterized in that the second free end of thehook has a bent-away free end essentially perpendicular to thelongitudinal axis of the shaft portion.
 8. The hook of claim 1,characterized in that the hook is formed as a pedicular hook.
 9. Thehook of claim 1, characterized in that the shaft portion has a clampingdevice adapted to fix the support rod perpendicular to the longitudinalaxis of the shaft.
 10. The hook of claim 1, wherein the hole has aconical section adapted to accept a screw provided with a conical head.11. The hook of claim 1, wherein the second free end of the hook isprovided with a bay dividing the second free end into two legs.